assistant: Require user to accept TOS for cloud provider (#16111)

This adds the requirement for users to accept the terms of service the
first time they send a message with the Cloud provider.

Once this is out and in a nightly, we need to add the check to the
server side too, to authenticate access to the models.

Demo:


https://github.com/user-attachments/assets/0edebf74-8120-4fa2-b801-bb76f04e8a17



Release Notes:

- N/A

crates/language_model/src/language_model.rs

@@ -9,7 +9,9 @@ pub mod settings;
 use anyhow::Result;
 use client::{Client, UserStore};
 use futures::{future::BoxFuture, stream::BoxStream};
-use gpui::{AnyView, AppContext, AsyncAppContext, Model, SharedString, Task, WindowContext};
+use gpui::{
+    AnyElement, AnyView, AppContext, AsyncAppContext, Model, SharedString, Task, WindowContext,
+};
 pub use model::*;
 use project::Fs;
 use proto::Plan;
@@ -114,6 +116,12 @@ pub trait LanguageModelProvider: 'static {
     fn is_authenticated(&self, cx: &AppContext) -> bool;
     fn authenticate(&self, cx: &mut AppContext) -> Task<Result<()>>;
     fn configuration_view(&self, cx: &mut WindowContext) -> AnyView;
+    fn must_accept_terms(&self, _cx: &AppContext) -> bool {
+        false
+    }
+    fn render_accept_terms(&self, _cx: &mut WindowContext) -> Option<AnyElement> {
+        None
+    }
     fn reset_credentials(&self, cx: &mut AppContext) -> Task<Result<()>>;
 }